Signaling system



mlg., y C. VVHKTE SIGNALING SYSTEM Filed May 5. 1921 2 mmm-Smm 1 ABELwm@

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AC3. WHIITE SIGNALING SYSTEM .2 Emma-www 2 Filed' May 5. 192k Patented.it-tug. i2, i924.

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CHARLES WHITE, OF EAST ORANGE, NEVI JERSEY, .[iSSG-NOR TO /VES'IERNELEOTBJIC COMPANY, INCORPORATED, F NEVI YORK, N. Y., A COR'QRATION OFNEWT YRK.

SIGNALNG- SYSTEM.

Application filed May 5,

To all whom t may concern:

Be it known that l, CHAnLns VVrIr'rn, a citizen of the United States,residingiatltast Grange, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in Signaling Systems,of which the following is ar full, clear, concise, and exactdescription.

This invention relates to signaling systems having separate transmissioncircuits for oppositely directed signals, commonly known as four-wiresystems, and more particularly to such systems wherein means areprovided at an intermediate station for the operator or attendant tolisten-in and to conmiunicate thereover, if desired.

ln ordinary telephone systems and in carrierv wave signaling systemswhich terminate in two-wire low frequency telephone lines, it has beencustomary to provide means for the operator or attendant to listeninand, if need be, to communicate over the systems. For the purpose oflistening-in on those systems a. telephone receiver with suitableapparatus is connected across the. low frequency line by means of amonitoring key. For communication purposes a micro-phone circuit can beconnected to the low frequency line in any suitable way, preferably bymeans of a patching cord.

3y this invention means is provide wheren by an operator or attendantmay listen in on a four-wire telephone line, or on a fourivire lowfrequency termination of a carrier wave signaling system. Means is alsoprovided whereby the operator or attendant may communicate over thesystem if desired.

@ne object of the invention is to provideJ means for listening-in andcommunie-ating over a four-wire low frequency telephone line. Anotherobject is to provide means of this kind at a four-wire termination of acarrier wave signaling system. Still another object is to providemonitoring system wherein the operator or attendant can listen-in onboth pairs of the four-wire line simultaneously. Ar feature of theinvention is the use of a conjugate transformer Vto accomplish the aboveresults. An other feature is the .provision of a relay arrangement forautomatically associating the microphone with lthe proper pair of' thefour-wire line 1921. Serial No. 456,932.

for talking and the receiver with the proper pair, for receiving whencommunicating` over the system. Still another feature is the provisionof a system which can be used for communicating either over a fonrsviresystem or a. two-wire system.

in one embodiment of the invention a carrier wave signaling systemterminates in a four-wire low frequency telephone line. By means of ahey, a conjugate transformer or hybrid coil and a plug and jackarrangement, a tele-phone receiver and a microphone are adapted to beconnected to the low frequency line. The arrangement is such that anoperator or attendant may listen-in on bot-h pairs of conductorssimultaneously without causing interference therebetween or he maycommunicate either over the carrier system or over the four-wire low frequency line. Aln order to insure that his receiver and microphone willeach be connected to the proper pair of conductors, an automatic relayswitching system is provided. Further provision is made for using thesame system in connection with a twoway carrier channel and itsassociated low frequency line.

rthe invention will now be described more in detail with reference tothe accompanying drawings. Fig. l shows the preferred form of theinvention as embodied in a four-wire carrier wave terminal station. Fig.la illustrates a two-way carrier terminal with twoe wire low frequencytermination located at the station of F l with which the arrangement ofl is adapted to be used. Fig. 2 shows another embodiment also adaptedfor use in a. four-wire system. it is to be understood that th-edetailed description does not limit the invention to the preciseembodiments illustrated. Y

Referring now to Fig. l of the drawing, a. four-wire low frequencytelephone line, comprising one pair of conductors 5 and another pair G,is connected by means of a. carrier wave terminal station to a commontransmission line l/iL, rEhe conductors 5 terminate in a pair of jacks7. The transmitting circuit TC of the carrier terminal stationterminates, on the low frequency side, in jacks 8 and, on the highfrequency side, at the bridge connections of balanced transformer 9. Abalancing network HFPL to balance the main line ML, is also connected tothe balanced transformer 9 in a well-known manner. Jacks 7 and 8 areconnected'together in such a way as normally to furnish a continuouscircuit between conductors and transmitting circuit TC. Conductors 6terminate in acks 10. Receiver circuit RC is connected, on the lowfrequency side, to jacks 11 and on the high frequency side to theseries'winding of the balanced transformer 9. Jacks and 11 are soconnected together that normally a continuous thej dotted lines 17. Y

vchannel Vis shown, but any number may be circuit is provided betweenconductors 6 and the receiver circuit RC.

' The other end of the four-wire low frequency line 5 6 terminates in atwo-Wire ordinary telephone exchange or subscribers stat-ion'A. Theconductors 5 and 6 are conjugately connected to station A through thebalanced transformer 12 with its low frequency balancing network LFN.This is a well-known arrangement and needs no further descriptio-n.

In the transmitting circuit TC is a modulator M, an oscillator O, amodulator band filter MBF, and an input transformer 15. The oscillator Ofunctions as a source of carrier Waves for this channel. VThe receivercircuit comprises a detector band -filter DBF, a detector D, a detectoramplifier DA, a low pass filter LPF yand a transformer 16. f

The modulator M, the oscillator C, the detector D and the detectoramplifier DA. may be of any suitable design, but preferably comprisethree electrode thermionic vacuum discharge devices. The modulator bandfilter MBF Iand detector band filter DBF are broad band-pass filters ofthe general type described in Patents Nos. 1,227,113 and 1,227,114 to G.A. Campbell, May 22, 1917. These filters are adapted to .pass a band offrequencies equal to the quency and of all lower frequencies,

Connections for additional transmitting channels are indicated by thedotted lines 16, and additional receiving channels by Only oneadditional inserted in a. similar manner.

In the operation of this system `a terminal Vstation similar to the oneillustrated is located at the distant end of the common line ML.V Thereceiving circuit of that station is adapted to cooperate with thetransmitting circuit of the terminal illustrated, while the transmittingcircuit of the distant station is adapted to cooperate with thereceiving circuit of Fig. 1.

A message may be transmitted from the station A to the distantcooperating station as follows:

Voice currents originating at station A are transmitted by the balancedtransformer 12 and conductors 5 through normally closed contacts ofjacks 7 and 8 and the transformer 15 to the modulator M. In themodulator M carrier waves from the oscillator C are modulated by theincoming voice current-s and transmitted from the modulator through themodulator band filter MBF and the balanced transformer 9 to the mainlin@ ML. Assuming now for purposes of description that the station ofFig( 1 is `the cooperating distant station, the modulated carrier wavesfrom the common line ML are transmitted to the receiving` circuit RC bythe balanced transformer 9 through the detector band filter DBF to thedetector D. In the system illustrated both the modulated and unmodulatedcurrents are transmitted to the common line ML and received therefrom.In the detector D the modulated and unmodulated currents are combined toproduce the original voice currents which are amplified in the detectoramplifier DA and transmitted through the low pass filter LPF,transformer 16, normally closed contacts of jacks 11 and 10, conductors6 and the balanced transformer 12 to the station A.

In order to provide for 'monitoring or listening-in by the operator orattendant at the carrier termin-al station, a monitoring key K and aconjugate transformer or hybrid coil 2O are used to associate atelephone receiver 26 with the low frequency conductors of each of thetransmitting` circuit TC and the receiving circuit RC. When key K isoperated, conductors 2l bridged across the transmitting circuit TC areconnected through the upper closed contacts (normally open) of key K andthe transformer 22 to the series winding of hybrid coil 20. Conductors2B which are bridged across the receiving circuit RC are connectedthrough the lower closed contacts (normally open) of key K and thetransformer 24 to the bridge terminals of hybrid coil 20. Ilelay 25 isoperated by the operation of key K due to the closing of the energizingcircuit of relay 25 at the lowest closed contact (normally open) of keyK. This circuit may be traced from the ground side of battery 27,through battery 27, winding of relay 25, lowest closed contact (normallyopen) of lrcy K to ground. The operation of relay 25 connects receiver26 with the line terminals of hybrid coil 20 at the closed frontcontacts (normally open) of relay 25. Across the opposite line terminalsof hybrid coil 2O is connected an impedance 23 which balances theimpedance oliE receiver 26. With the key K in its normal position,receiver 26 and hybrid coil 2O are disconnected from the carrierterminal apparatus.

By means ot the monitoring[circuit just described an operator listeningin at the receiver 26A can hear what is going on on either thetransmitting circuit TC or the receiving circuit RC, but dueto theconjugacy of hybrid coil 20, current in conductors 2l has no effect uponconductors 23 and vice versa. Consequently, a monitoring system isprovided for a tour-wire low frequency telephone circuit whereby anoperator muy listen-in simultaneously on each pair ot conductors withoutcausing interference between the pairs ot conductors.

.ln order to provide tor communication over the system by the operatoror attendant, the aplaratus now to be described is provided. y

For receiving` purposes, receiver 26 is connected to jacks 3l throughthe normally closed back contacts ot relay 25, normally closed contactsot key KT and the normally closed haci( contacts ot relay 32. AFortalking purposes, microphone is associated with jacks 34 through aninduction coil normally closed contacts of ringing vkey RK and normallyclosed back contacts ot relay 36. ln order to provide for call signalingby the operator, a source ot ringing current 37 is adapted to beimpressed upon `the system hy means of ringing key RK. A twoconductorcord 3S, terminating in plugs 39 and 40 is adapted to patch the circuitsterminating' in jacks 3l to those terminating` in either jacks 7 or 8.The three-conductor cord 4l, terminating in plugs 42 and 43 is adaptedto patch the circuits terminating in jacks 34 to those terminating ineither jacks l0 or ll.

Relays 32 and 36 Aare provided to automatically interchange jacks 31 and34 with respect to the receiver 26 and the micro phone 33. ln the normalposition ot' relays 32 and 36, receiver 26 is connected to jacks 31, and`microphone 33 to jacks 34 over' the circuits hereinhetore traced. lWhenrelays `32 and 36 are actuated, receiver 26 is connected to jack 34through the normally closed hack contacts of relay 25, normally closcdcontacts ot key KT and the closed itront contacts (normally open) ofrelay 32, while the microphone 33 is connected to jacks 3l through theinduction coil 35, the normally closed contacts of ringing key RK andthe closed front contacts (normally open) ot relay 36.

The operation of communi-eating Jfrom the carrier terminal station tothe station A will. now be described. Jacks 3l and 7 arr patchedtogether loy means et cord 38 hy the insertion of pings 39 into jacks'i' and plugs 40 into jacks 31. Jacks l0 and 34 are patched together bymeans ot cord 41 by the insertion off plugs 43 into jacks 16 and plugs42 into jacks 34. it message originating at station fi. is transmittedto receiver 26 through the conjugate transformer l2, conductors 5, tipconnections of jacks 7 and plugs 39, conductors ot cord 33, tipconnections of plugs 40 and jacks 3l, normally closed back contacts ofrelay normally closed contacts of key KT and normally closed backcontacts ot relay A. message originating at the carrie-r terminalstation in microphone is transmitted to station A through the inductioncoil 35, normally closed contacts of ringing key ltli, normally closedback contacts ot relay tip connections oit jacks 34 and plugs 42., tipconductors of cord 4l, tip connections of plugs 43 and jacks l0,conductors 6 and bridge connections ot conjugate transformer l2. Theinsertion of plugs 39 in jacks T and plugs 43 in jacks lO, disconnectsthe conductors 5 and 6 trom the carrier transmitting circuit TC andreceiving circuit it@ respectively at the open contacts (normallyclosed) ot jacks and 10.

In the event that the opera-tor a t vthe carrier station wishes tocommunicate by means of carrier wave transmission over the main line MLinstead of with the station plugs 39 are withdrawn from jacls 7 andinserted in jacks' 3 and plugs 43 are withdrawn from jacks l() andinserted in jacks il. The insertion of plugs 43 in jacks ll causes theoperation of relays 32 and 36 so that re ceiver 26 is now connected tothe receiver circuit RC and the microphone 33, to the carriertransmitting circuit TC. The energizing circuits' ot relays 32 and 36entend from the ground side of batteries 44 and 45 respectively, throughthose batteries, wind ings of relays 32 and 36 in parallel to thenormally closed left-hand contact ot' key KT, through the sleevecontacts ot jacks 34 and plugs 42, through the sleeve conductor of cord41, the sleeve contacts ot plugs 43 and jacks 1]., and the resistance 46to ground.

The message circuit between the carrier terminal station and a distantcooperating station may he traced as follows:

A, message originating in the microphone 33, after passing through theinduction coil 35, normally closed contacts oit ringing key RK, closedfront contacts (normally open) oft relay 36, tip connections ot' jacksand plugs 40, conductors ot cord 33, tip connections of plugs 39 andjacks 8 and trans ltormer 15, modulates the carrier current `tromoscillator From the modulator M it passes through the band filter li/BFand the conjugate transformer 9 as modulated llO energy to the main lineML. Modulated energy incoming from the main line ML passes through theconjugate transformer 9 and detector band filter DBF to the de tector D,where the originating voice currents are detected. vafter amplificationby the detector amplifier DA, they pass through the low pass filter LPF,transformer 16, tip connections of jacks 11 and plugs 43, tipconductorsy of cord Ll1, tip connections of plugs 42 and jacks 84e,closed front contacts (normally open) of relay 32, normally closedright-hand contacts of key KT, and normally closed back conta-cts ofrelay 25 to the receiver 26.

Tf the operator should by any chance interchange plugs 89 and 48 byinserting plugs 89 in jacks 11 and plugs 48 in jacks 8, relays 32 and 36would not be operated since there would be no ground connection from thesleeve of jacks 8. Still the message cirrcuit would be correct since themicrophone 83 would be connected to the carrier transmitting circuit TCand the receiver 26 would be connected to the carrier receiver circuitRC. The transmitting circuit, under this condition, may be traced fromthe microphone 38, through the induction coil 35, the normallyl closedcontacts of ringing key RK, normally closed back contacts of relay 3G,the tip connections of jacks 811- and plugs 42, tip conductors of cord4:1, tip connections of plugs 113 and jacks 8, which jacks constitutethe terminal of' the transmitting circuit TC. The receiving circuit maybe traced from the receiver 26 through the normally closed back contactsof relay 25, vthe normally closed right-hand contacts of key KT, thenormally closed back contacts of relay 82, tip connections of jacks 31and plugs 40', conductors of cord 38, tip connections of plugs 89' andjacks 117 which jacks constitute the termination of the receivingcircuit RC.

ln order to provide for communication from the carrier terminal stationover a two-wire low `frequency line or over a twoxvay carrier channelterminating on the low frequency side in a twoiwireV line, key KTprovided. lts use will be described hereinafter 'in connection with Fig.l?.

In Fig. 2, a modified system is provided whereby an operator orattendant at a carrier terminal station mayvcommunicate in eitherdirection over the four-wire system of Fig, 1. Like reference charactersin all of the figures are used to designate like elements.

The connections of relays 32 and 36to jacks 31 and 34 in Fig. 2, areidentical with the connections of these elements in Fig. 1. Instead ofconnecting lthe receiver directly to the armature contacts of relay 82and the transmitter directly to the armature contacts of relay 35, anoperators subset comprising a microphone 51, a receiver 52 and aninduction coil 53 are associated with the armature conta-cts of relays32 and 3G through the conjugate transformer 50. The operators subset isconnected to one set of line terminals of the transformer 50 and isbalanced by a network CN connected to the opposite pair of terminals.rlhe direction in which transmission takes place through this circuitarrangementis shown by arrows.

lVhen the arrangement of Fig. 2 is used with the transmission system ofFig. 1, jacks 31 and 34C are patched to jacks and 10 or 8 and 11 inexactly the same manner as hereinbefore described and the resultsaccomplished are entirely similar. .Further detailed description of theconnections and the operation of the system is therefore not required.

ln Fig. 1a is shown a two-way carrier wave transmission systemterminating in a two-wire low frequency line whereby conversation may becarried on between an ordinary telephone subscribers subset or telephoneexchange B and a distant cooperating station over a common transmissionline ML. The lines ML are separate physi ca` lines which terminate atthe same station where the carrier apparatus of Figs. 1 and 1 arelocated. The station B is connected to the carrier terminal station by aline 54: terminatingl in jacks 55. The low frequency terminals of thetransmitting circuit T C and receiver circuit RC are conjugatelyconnected by means of the conjugate transformer 5G to the two-wirecircuit terminating in jacks 57. Normally a continuous circuit isprovided from the conjugatc transformer 56 to the low frequency line 5ethrough the normally closed contacts of jacks 57 and 55. A low7frequency network LFN to balance the/low frequency line 54 is normallyconnected to the conjugate transformer 56 through the normally closedback contacts of relay 58. The eh ments in the carrier transmittingcircuit TC and in the receiver circuit RC may be identical with thosedescribed iu connection with Fig. 1 and are connected to the main lineML in an identical manner.

Let it be assumed now that an operator or attendant at the carrierterminal of Fig. 1 wishes to connnunicatc with a party at station B. Thekey KT will be thrown to its operated position and jacks 84 will bepatched to jacks 55 by the insertion of plugs 4-2 in jacks 3st and plugs4?), in jacks 55. The insertion of plugs 43 in jacks 55 disconnects thecarrier terminal apparatus from the line 5ft at the open contacts(normally closed) of jacks 55. The operation of key KT disconnectsrelays 82 and 3G from the sleeves of jacks 34. at the normall;T closed(now open) left-hand contact of key KT and connects relay 59 to the lll)Leos/ice sleeves of jacks 34. Relay 59 is not operated, however, sinceits energizing circuit is open at the sleeves ofjacks 55. The functionof relay 59 will be hereinafter described. The operation of key KT alsodisconnects receiver 26 from jacks 3l at the right-hand open contacts(normally closed) and connects the receiver 26 to the bridge points ofthe operator-s telephone set through the normally closed back contactsof relay and the closed (normally open) right-hand contacts of key KT. l

message originating at station B reaches the receiver 26` over the line54, tip` connections of jacks and plugs 43, tip` conductors of cord 4l',tip connections of plugs 42 and jacks 34, normally closed back contactsof relay 36, normally closed contacts of ringing key RK, normally closedback contacts of relay 59, bridge connections of the operators telephoneset, righthand closed contacts (normally open) of key KT and normallyclosed back contacts of relay 25. A message originating at microphonereaches the station B through the induction coil 35 Vand the circuitjust traced except that practically none of the current reaches thelreceiver due to the anti-side tone connection of the operatorstelephone set.

ln order that the operator or attendant at the carrier telephone stationof Fig. l may communicate over the two-way channel of the carrierterminal station of Fig. la, plugs 43 are withdrawn from jacks 55 andinserted in jacks 57. Due to this operation,l relays 58 and 59 areoperated by current in an energizing circuit which may be traced fromthe ground side of battery 60, through battery 60, winding of relay 59,left-hand closed contact (normally open) of key KT, sleeve contacts ofjacks 34 and plugs 42, sleeve conductor of cord 41, sleeve contacts ofplugs 43 and jacks 57, winding of relay 58 to ground. The operation ofrelay 59 has the effect of insertingl a resistancel 62 in the lowerconductor of the operators telephone circuit by removing a shortcircuitabout the resistance 62 at the open contact (normally closed) of relay59 and connect-- ing a resistance element 6l across this circuit theclosed front contact (normally open) of relay 59. Resistance elements 62and 6l when so connected operate as an artificial line of a certainlength depending upon thel values of the resistances 62 and 6l, Theoperation of relay 5S substitutes a network MN to balance the operatorstelephone circuit in place of the low frequency network LFN whichnormally balances the low frequency line 54. The function of theartificial line is to reduce the effect upon the conjugate transformer56 of impedance changes in the microphone 33 of the operaltors telephonecircuit and so to permit lof maintaining the required balance by meansof a fixed network MN. By the substitution of network MN for thenormally connected network LFN, a simple artici al line, such as isprovided `by the resista-nces 6l and 62, may be used.

l'lxhile the invention has been described in connection with carriercurrent lterminal stations, it is equally applic-able to ordinaryfour-wire telephone circuits. lts application to such a circuit will beobvious to those skilled in the art from the descrip- Ition of itsapplication to the low frequency four-wire termination of a carriercurrenttelephone system and further description will, therefore, not begiven.

'The scope of the invention is understood to be defined by the appendedclaims.

1iWhat is claimed is:

l. In a telephone system, a four-wire line, a telephone receiver, aconjugate transformer, means to connect said receiver to' said conjugatetransformer, meansto connectsaid conjugate transformer to the fourwireline, and means to cause connection of the receiver to the conjugatetransformer whenever the conjugate Itransformer is connected to thefour-wire line.

2. In a telephone system, a four-wire line, a telephone receiver, aconjugate transformer, a relay to connect said receiver to saidconjugate transformer, and `a key to connect the conjugate transformerto the four-wire line.

3. In a telephone system, a four-wire line, a telephone receiver, aconjugate trans former, a relay `to connect the receiver to theconjugate transformer, a key to connect the conjugate transformer tothefourwire line, and means to cause the operation of the relay wheneverthe key is operated -to connect the conjugate transformer to thefour-wire line.

4. ln a telephone system, a four-wire line, a telephone receiver, aconjugate coil, means to connect the receiver to the conjugate coil,means tol connect the conjugatecoil to the four-wire line, means tooperate the receiver-connect-ing means whenever the. conjugate coil isconnected. to the four-wire line, and an impedance connected to theconjugate coil to balance the telephone receiver. l

5. ln a telephone system. a telephone receiver, a conjugate coil, arelay to connect the receiver to the conjugate coil, a key to connectthe conjugate coil to the four-wire line, and an impedance connected tothe conjugate coil to balance the telephone receiver.

6. In a telephone system, a telephone receiver, a conjugate coil` arelay to connect the telephone receiver to the conjugate coil when therelay is energized, a key adapted when operated to connect the conjugatecoil to the four-wire line, means to energize the relay effectiveWhenever the key is operated, and an impedance connected to theconjugate coil to balance the telephone receiver.

7. ln a telephonel system, a four-wire line comprising two pairs ofconductors, a. telephone receiver, a conjugate coil, a series Windingfor said conjugate "coil, a bridge connection for said coil, means toconnect the series Winding to one pair of conductors, means to connectthe bridge Winding to the other pair of conductors, and'means to connectthereceiver to the conjugate coil Whenever the series Winding and bridgeconnection of the conjugate coil are connected each to a pair ofconductors of the four-Wire line.

8. In a telephone system, a four-Wire line comprising-'two pairs ofconductors, a telephone receiver, a conjugate transformer, a seriesWinding for said transformer a bridge connection for said transformer,means to connect the receiver to the conjugate transformer, and a keyadapted to, connect the series Winding to one pair and the bridgeconnection to another pair of said four- Wire line and to cause theconnection of the telephone receiver to the conjugate transformer.

9. In a telephonesystem, a four-Wire line comprising tivo pairs ofconductors, a teleT phone receiver, a conjugate transformer, a seriesWinding and a bridge connection for said transformer, a relay adapted toconnect the receiver to the conjugate transformer, and a key adapted toconnect the series Winding and the bridge connection each toa pair ofconductors of the four- Wire line and to cause the energization of therelay to connect the receiver to the conj ugate coil.

10. In a telephone system, a four-Wire line comprising` two pairs ofconductors., a telephone receiver, aconjugate transformer, a seriesWinding for said transformer, a bridge connection for said transformer,a

1elay adapted to connect the receiver to they transformer, a key adaptedto connect the series Winding to one pair and the bridge connection toanother painof conductors of said four-Wire line and to cause theactuation of the relay to connect the receiver to ceiving circuit, meansto connect said circuits to a common line, a telephone receiver, aconjugate transformer, means to conjugately connect said transformer tosaid transmitting and receivingcircuits, and means to connect saidreceiver to said conjugate connecting means, operative whenever saidconjugate connective means is actuated.

13. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit. means to connect said cnrriercircuits to a common line, a telephone receiver, a `conjugatetransformer, a series Winding for said conjugate transformer, a bridgeconnection for said transformer, means to connect the series windingwith the carrier transmitting circuit, means to connect the bridgeconnection ivith the carrier receiving circuit, and means to connect thereceiver With the conjugate transformer Whenever the series Winding andbridge connections are connected to the carrier transmitting circuit andthe carrier receiving` circuit respectively.

111-. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit, means to connect said circuits toa carier transmission line, a telephone receiver, a conjugatetransformer, a. series windingfor said transformer, a bridge connectionfor said transformer, means adapted to connect the receiver to theconjugate transformer, and a kej7 adapted to connect the series Windingto the carrier transmitting circuit and the bridge connection to thecarrier receiving circuit respectively and to cause the actuation of thereceiver-connecting` means.

1:3. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit, a telephone receiver, a conjugatetransformer, a series winding for said transformer and a bridge windingfor said transformer, a relay adapted upon energization to connect thetelephone receiver to the conjugate transformer, and a key adapted uponactuation to connect the series winding` to the carrier transmittingcircuit and the. bridge connection to the carrier receiw ing circuit andto cause the energization of said relay.

16. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit, a telephone receiver, a conjugatetransformer, a series winding` for said transformer and a bridgeconnection for said transformer, a relay adapted upon encrgization toconnect the telephone receiver to the conjugate transformer, a keyadapted upon actuation to connect the series Winding to the carriertransmitting circuit and the bridge Winding to the carrier receivicircuit and to cause the energization of said relay, and an impedanceconnected Cil to the conjugate transformer to balance the telephonereceiver.

17. In a telephone system, a four-wire line, a receiving circuit andtransmitting circuit at a monitoring station, means adapted to connectsaid receiving circuit and said transmitting circuit to the tour-wireline,

and automatic switching means to interchange the relative connection otsaid transmitting and receiving circuits.

18. In a telephone system, a tour-wire line comprising two pairs ofconductors, a receiving circuit and a transmitting circuit at amonitoring station, means adapted to connect said receiving circuit toeither pair of conductors, means to connect said transmitting circuit tothe other pair ot said conductors, and automatic switching means tocause the receiving circuit and transmitting circuit to loe connectedrespectively to the same pair of conductors independently of the way inwhich said receiving and trans'- mittiiig connecting means are connectedto said conductors.

19. ln a telephone system, la tour-wire line comprising two pairs ofconductors, a receiving circuit and a transmitting circuit at amonitoring station, means to normally connect the receiving circuit toone pair of conductors and other means to normally connect thetransmitting circuit to the other pair of conductors, and switchingrelays automatically energized to connect the receiving andtransmittingcircuits respectively to the same pair or" conductorswhenever the receiving and transmitting connecting means areinterchanged.

20. Ina telephone system, a tour-wire line comprising two pairs otconductors, a receiving circuit and a transmitting circuit at amonitoring station, means to normally connect the receiving circuit toone pair oit conductors and other means to connect the transmittingcircuit to the other pair oi conductors, and switching relaysunall'ected by the normal connection or' said transmitting andreceiving` connecting means and adapted to interchange said transmittingand receiving circuits it the transmitter and receiving connecting meansare reversely connected to said pairs ot conductors.

21. In a telephone system, a tour-wire line comprising tivo pairs ofconductors, a receiving circuit adapted to he normally connected to onepair oi conductors and a transmitting circuit adapted to he normallyconnected to the other pair of conductors, a pair ot jacks normally7connected to said transmitting circuit, another pair of jacks normallyconnected to said receiving circuit, means to connect saidfirst-mentioned pair of jacks to one pair of conductors, means toconnect said second pair ot jacks to the other pair of conductors, andswitching means between said liacks and said receiving and transmittingcircuits to interchange said jacks with respect to said transmitting andreceiving circuits whenever said connecting means are reverselyconnected to said pairs oli conductors.

22. ln a telephone system, a :tour-wire line comprising two pairs ofconductors, a receiving circuit anda transmitting circuit at amonitoring station, a pair of jacks normally connected to said receivingcircuit and a pair ot jacks normally connected to said transmittingcircuit, means to normally connect said receiving ack with one pair otconductors, means to normally connect said tiansi'nitting jack with theother pair oitl conductors, and a switching relay connected between saidreceiving and transmitting jacks and said receiving and transmittingYcircuits to interchange said jacks with r'- spect to said receivingandtransmitting circuits it said connecting means are reversely connectedto said pairs et con ductors.

23. In a telephone system, a four-wire line comprising a pair otconductors for transmitting and a second pair of conductors forreceiving, a pair ot cut-oil1 jacks in said transmitting conductors, apair of cut-oft jacks in said receiving conductors, a receiving circuitand a transmitting circuit at a monitoring station, a pair ofreceivingjacls normally connected to vsaid receiving circuit, a pair oftransmitting jacks normally con.- nected to said transmitting circuit, apatching cord adapted to normally connect said receiving jacks with saidcut-oil jacks in the 'transmit-ting pair of conductors, another patchingcord adapted to normally connect said transmitting jacks with saidcut-oil' jacks in the re .eiving pair of conductors, and switching meansadapted to automatically interchange said receiving and transmittingjacks if said transmitting jacks are patched to said cut-oil7 jacks inthe transmitting pair of conductors.

24. in a telephone system, a ifouifwireline comprising a pair oiconductors tor transmitting and a second pair ot conductors forreceiving, a pair ot cut-oil jacks in said transmittingconductors, apair oi cut-oil jacks in said receiving conductors, a receiving circuitand a transmitting circuit at a monitoring station, a pair of receivingjacks normally connected to said receiving circuit, a pair oftransmitting jacks normally connected to said transmitting circuit, apatching cord adapted to normally connect said receiving jacks with saidcut-oi'f jacks in the transmitting pair ot conductors, another patchingcord adapted to normally connect said transmitting jacks with saidcut-olf acls in the receiving pair of conductors, and switching meansadapted to automatically interchange said receiving and transmittingjacks if said jacks are revers'ely lili patched to the cut-off jacks insaid transmitting and receiving pairs of conductors.

25. In a telephone system, a four-Wire line comprising a pair ofconductors for transmitting and a second pair of conductors forreceiving, a pair of cut-off a-cks in said transmitting conductors, apair of cut-off jacks in said receiving conductors, a receiving circuitand a transmitting circuit at a monitoring station, a pair of receivingjacks normally connected to said receiving circuit, apair oftransmitting jacks normally connected to said transn'iitting circuit, apatching cord adapted to normally connect said receiving jacks with saidcut-oilz jacks in the transmitting pair of conductors, another patchingcord adapted to normally connect said transmitting jacks with saidcut-ott jacks in t-lie receiving pair of conductors, and relay contactsconnected in circuit between said receiving and transmitting jacks andsaid receiving and transmitting circuits adapted to interchange saidtransmitting and receiving jacks with respect to said transmitting andreceiving circuits if said transmitting and receiving jacks arereversely connected tov said cut-off acks in the transmitting andreceiving pairs of conductors.

26. In a carrier current telephone system, a carrier terminal station, areceiving circuit and atransmitting circuit at said terminal station,means adapted to connect said receiving and transmitting circuits tosaid carrier terminal station, and automatic switching means tointerchange the connections of saidi transmitting andreceiving circuits.

27. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit, means to connect said circuits toa carrier transmission line, a receiving circuit and a transmitting`circuit at a carrier terminal station, means to connect said receivingcircuit to said carrier transmitting circuit, other means to connectsaid transmitting circuit to said carrier receiving circuit, andautomatic switching means to interchange the connection of saidreceiving and transmitting circuits to said carrier transmitting andreceiving circuits respec-v .means and said transmitting and receivingcircuits adapted to interchange said transmitting and receiving circuitsif said connecting means are reversely connected to said carriertransmitting and receiving circuits.

29. In a carrier current telephone system, a carrier terminal station, acarrier transmitting circuit, a carrier receiving circuit, a telephonetransmitting circuit and a telephone receiving circuit all at saidcarrier terminal station, means to connect said telephone receivingcircuit to said carrier transmitting circuit, other means adapted toconnect said telephone transmitting circuit to said carrier receivingcircuit, and switching relays adapted to interchange said transmittingand receiving circuits whenever said connecting .means are rcverselyconnected to said cariier transmitting and receiving circuits andoperated whenever said connecting means are actuated.

30. In a carrier current telephone system, a carrier transmittingcircuit, a carrier receiving circuit, a telephone receiving and atelephone transmitting circuit at the carrier terminal station, a pairof receiving jacks normally connected to said receiving circuit, a pairof transmitting jacks normally connected to said transmitting circuit,means to connect said receiving jacks to said carrier transmittingcircuit, means adapted to connect said transmitting acks to said cai'-rier receiving circuit, and switching means between said jacks and saidreceiving` and transmitting circuits adapted to interchange saidreceiving and transmitting circuits whenever said connecting means arereversely connected to the carrier transmitting and receiving circuits.

3l. In a telephone system, a four-wire line, a two-wire line, areceiving circuit and a transmitting circuit at a monitoring station,means to connect said transmitting and receiving circuits to saidfour-wire line, means to connect said transmitting circuit to saidtwo-wire line, and means operative upon such a connection to connectsaid rcceiving circuit to said transmitting circuit in operativerelation with said tivo-wire line.

32. In a telephone system, a four-wire line, a two-wire line, receivingand transmitting circuits at a monitoring station, means to connect saidreceiving and transmitting circuits to the four-wire line, means toconnect said transmitting circuit to said tivo-wire line, and a keyadapted to connect said receiving circuit to said transmitting circuitin operative relation for telephone use with said two-wire line.

33. The method of signaling in a carrier wave system having a stationtern'iinating in a four-Wire low frequency line, which method comprisestransmitting signals over the low frequency line and listening-iiisimultaneously on each pair of conductors of the low frequency linewithout causing interference therebetween.

34. In a signaling system, two pairs of transmission conductors, meansfor impressing voice frequency signals upon each pair Sil lti.)

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of conductors, and means tor listening-in simultaneously on each pair ofconductors without causing interference therebetween.

35. In a signaling system, two pairs of voice current conductors, twopairs of car rier current conductors electrically connected to saidfirst pairs of conductors respectively, means for impressing voicefrequency signais upon each pair of conductors, and means forlisteningin simultaneously on each pair et conductors without causinginterference therebetween.

36. In a signaling system, two pairs of voice current conductors, twopairs of carrier current conductors, means electrically connecting saidvoice current pairs with said carrier current pairs respectively, andmeans for monitoring a conversation in both direc tions simultaneouslywithout mutual inten ference between said pairs carrying oppositelydirected elements of said conversation.

37. In a signaling system, a terminal station, a second station, twopairs ot voice frequency lines extending between said stations, a sourceof carrier current and a detecting means connected to said pairs ot'lines respectively at said second station, and means for monitoring aconversation in both directions simultaneously without mutualinterference.

In witness whereof, I hereunto subscribe my name this 3rd day of May, A.D., 1921.

CHARLES WHITE.

